ATF38143 Agilent(Hewlett-Packard), ATF38143 Datasheet - Page 9

• Manufacturer Part Number: ATF38143
• Description: Low Noise Pseudomorphic HEMT in a Surface Mount Plastic Package
• Manufacturer: Agilent(Hewlett-Packard)

Noise Parameter
Applications Information
F
are based on measurements while
the F
extrapolated. The F
based on a set of 16 noise figure
measurements made at 16
different impedances using an
ATN NP5 test system. From these
measurements, a true F
calculated. F
true minimum noise figure of the
device when the device is pre-
sented with an impedance
matching network that trans-
forms the source impedance,
typically 50 , to an impedance
represented by the reflection
coefficient
design a matching network that
will present
minimal associated circuit losses.
The noise figure of the completed
amplifier is equal to the noise
figure of the device plus the
losses of the matching network
preceding the device. The noise
figure of the device is equal to
F
min
min
values at 2 GHz and higher
only when the device is
mins
below 2 GHz have been
o
min
. The designer must
o
to the device with
represents the
min
values are
min
is
presented with
tion coefficient of the matching
network is other than
noise figure of the device will be
greater than F
following equation.
NF = F
Where R
noise resistance,
mum reflection coefficient
required to produce F
the reflection coefficient of the
source impedance actually
presented to the device. The
losses of the matching networks
are non-zero and they will also
add to the noise figure of the
device creating a higher amplifier
noise figure. The losses of the
matching networks are related to
the Q of the components and
associated printed circuit board
loss.
higher frequencies and increases
as frequency is lowered. Larger
gate width devices will typically
have a lower
narrower gate width devices.
o
min
is typically fairly low at
n
+ 4 R
/Z
o
Zo (|1 +
is the normalized
min
n
o
as compared to
o
9
based on the
. If the reflec-
o
is the opti-
|
min
s
o
|
o
–
2
, then the
) (1 –
and
o
|
2
s
s
|
is
2
)
Typically for FETs, the higher
usually infers that an impedance
much higher than 50 is required
for the device to produce F
VHF frequencies and even lower
L Band frequencies, the required
impedance can be in the vicinity
of several thousand ohms.
Matching to such a high imped-
ance requires very hi-Q compo-
nents in order to minimize circuit
losses. As an example at 900 MHz,
when air-wound coils (Q > 100)
are used for matching networks,
the loss can still be up to 0.25 dB
which will add directly to the
noise figure of the device. Using
muilti-layer molded inductors
with Qs in the 30 to 50 range
results in additional loss over the
air-wound coil. Losses as high as
0.5 dB or greater add to the
typical 0.15 dB F
creating an amplifier noise figure
of nearly 0.65 dB. A discussion
concerning calculated and
measured circuit losses and their
effect on amplifier noise figure is
covered in Agilent Application
1085.
min
of the device
min
. At
o